Wavelength Division Multiplexing (WDM) uses a multiplexer at the transmitter to multiplex a number of optical signals with different wavelengths onto a single optical fiber, and a demultiplexer at the receiver to split them apart.
A WDM receiver usually comprises a collimator, a number of condensing lenses, and a light splitter. The light splitter comprises an array of filters and a mirror. Each filter corresponds to one condensing lens. In operation, a first filter receives incident light collimated by the collimator. Then, the first receiver allows the incident light in a particular wavelength band to penetrate towards the corresponding condensing lens and reflects the incident light in other wavelength bands towards the mirror, so that the incident light can be reflected by the mirror towards a second filter. The second filter performs the similar actions as the first filter, so that the incident light L can finally be split into light of different wavelengths after repeated penetrations and reflections.
However, since the excess incident light is repeatedly reflected by the mirror, the transmission distance and the transmission time period of the excess incident light increase, which may increase the optical loss. Optical loss of excess incident light at the last channel reaches a maximum value, which decreases the transmission efficiency of the WDM receiver.